This request is for funds to purchase two Ultramicrotomes with cryokits for use in the EM facility within the Center for Biologic Imaging (CBI) at the University of Pittsburgh. Immuno-electron microscopy, using ultrathin cryosections for immunogold labeling, is an essential service provided by the CBI, and the center has had two ultracryomicrotomes in continuous use since it first started operations in 1991. Initially the cryokits were both based around two UltraCut E units, one was new the other dated from the early 1980's. When one of these units failed it was kept for spare parts and replaced with an Ultracut S Cryokit some 13 years ago. 2 years ago the S-unit cryokit failed irreparably (Leica does not provide any support for these systems at all, and independent contractors were unable to repair the device due to multiple failures of the electronics and temperature control of the cryochamber). We have managed to keep the older UltraCut E unit running using spare parts harvested from the previously retired system, however this system which is now over 16 years old is failing and also cannot be repaired reliably, and certainly even with all day usage does not keep up with the needs of our user base. Essentially this system must be retired also. We will continue to use them as microtomes (in fact the Ultracut S unit is already fullfilling this role) but it is imperative we purchase 2 new cryosystems. Unfortunately this can only be done by purchasing complete ultramicrotomes plus cryokits due to manufacturing obsolescence. It is important to realize we really do need two systems, and are not simply requesting two devices to get above the funding floor of the SIG grant mechanism. Following failure of the first cryokit we were tempted to put in a "padded" application for a single cryoultramicrotome, however we felt that would be a little egregious. Now we are in a no-win situation where we must replace two systems (there are no other ultracryomicrotomes or core research EM facilities on campus or functioning ultracryomicrotomes in all of Pittsburgh). This need is defined in the description of the usage of the Center, the projected usage by individual users and in letters of support from senior institutional officials Public Health Relevance: Immuno-electron microscopy, using ultrathin cryosections for immunogold labeling, is an essential tool in defining exactly where proteins are within cells and tissues. The resolution is at least 10 times better than that possible using light microscopy. This resolution advantage makes this method an extremely important tool in understanding the molecular mechanisms underlying disease by defining where molecules of import are made and work within cells.